Adsorption and Desorption Kinetics of a Block Copolymer Wetting Agent Used in Copper Electroplating

Abstract

Current development of copper electroplating additives has led tothe development of suppressors that not only allow for proper bottom-upfill but also that wet the surface properly for defect-free entryof the copper-seeded wafer into the plating bath. The current workanalyzes the adsorption and desorption characteristics of a commonblock copolymer wetting agent using an electrochemical flow-throughcell. Adsorption characteristics are similar to that of polyethyleneglycol (PEG) during electroplating, where the adsorption processbecomes a strong function of polymer bulk concentration under 200ppm and where increasing applied potential or current causes thesurface suppression of the polymer to decrease. Desorption experimentsshowed similar results to PEG as well, where a two-stage desorptionis seen when the applied potential or current becomes large enough.Computation fluid dynamic modeling of the flow-through cell allowedfor the determination of the saturated surface coverage at -0.1 Vvs Ag/AgCl, which was 0.041 �g/cm2. Additionally, the adsorptionrate constant was modeled to be 6.02, 2.045, and 1.22�105 m3/kmols for applied potentials of -0.1, -0.15, and -0.2 V vs Ag/AgCl, assuminga constant saturated surface coverage of 0.041 �g/cm2.